The present invention relates to a new and improved construction of a continuous or throughpass leather working machine, especially an embossing and ironing machine for leather having at least one leather working element, particularly an embossing and/or ironing element in the form of a heated tube.
During the finishing of leather the production of an artificial, plastic (three-dimensional) surface at the leather (the so-called embossing operation) is an important working step. Up to now in practice this work was carried out in the tannery by means of large hydraulic pressing machines. These pressing embossing machines press large surface-steel embossment plates, during a cyclic operation and at high pressure and temperature, into the surface of the leather. The expenditure in work for this operation is extremely high because the pressing embossing work in a cyclic operation requires a great amount of time for closing the work space or compartment, to build-up pressure, for heating the leather, and again for opening the work compartment.
Up to now all attempts to overcome these drawbacks have failed to practice. The reason for this lack of success is primarily the cost outlay for the embossing elements in the form of embossing rolls which must be heated extremely well. Also the possibility of rapidly and simply exchanging such embossing rolls is an important factor in the tannery. There are completely different prerequisites for such embossing work when performed in a tannery than, for instance, in plants which process plastics where an embossed surface is applied by calenders to meter-long plastic webs which are available in large quantitites. During the operation of a tannery the adaptability of a pressing embossing machine should be extremely high. The actual embossing elements should be relatively economical in price, because the tannery processes large numbers of different patterns.
Different attempts have been made to solve these problems. Thus, for instance, in German Patent application No. P 22 45 018.6 there is disclosed an embossing surface in the form of a hollow roll which is heated from the outside and inside by means of a radiant heater. The embossing pressure is applied by means of one or a number of pairs of rolls, and of each roll pair one such roll is arranged outside and the other inside the hollow roll. Apart from certain advantages which can be realized with this equipment, nonetheless these machines are associated with the disadvantage that the hollow roll must have a relatively large diameter, so that it is possible to internally arrange the counter-pressure roll and the heater. The relatively thin wall of the hollow roll also causes difficulties when fabricating the embossing surface. Machines of this construction are therefore not extremely suitable for performing the actual embossing work.
In German Patent application P No. 25 43 526.1 there is proposed a solution wherein the embossing surface is arranged in the form of a long tube between two pairs of rolls or between one roller pair and a roll. These rolls support the roll-shaped embossing body against bending-through and which embossing body internally has an extremely small diameter. Between the rolls and the roll-shaped embossing body there are arranged elastic transport bands or belts which serve to transmit the embossing force from the roll-shaped embossing body to the support rolls and thus protect the embossing surface. In order to heat the leather there is provided a contact heater which, however, is located completely separate from the embossing zone at the infeed transport band where the leather, during its movement, is pressed against a smooth heated surface and is thus preheated. With this arrangement it would be possible to produce price worthy embossing elements. However a drawback which exists with such solution is that the comparatively small diameter of the tubular-embossing element does not permit installation of any efficient radiant heater, something necessary in practice. A further drawback associated with the small diameter of the embossing element is that during the embossing work the leather tends to adhere to the surface of the roll, and thus, the operator, with such small diameter of the embossing element, has too little time and possibility to tear away the adhering starting portion of the leather from the roll surface. Supporting the embossing tube with the aid of a second felt band is effective, yet however has the disadvantage that such proposal appreciably complicates the construction of the machine, quite apart from the wear exerted upon such support bands.